The present invention relates to an aluminum alloy material plate used for support members for offset printing or lithographic printing plate (hereinafter referred to as "Printing aluminum alloy material plate").
Heretofore, rolled plates having a plate-thickness of from about 0.1 to 0.5 mm, which satisfy the requirements of the Japanese Industrial Standard (JIS) A1050P, A1100P, A3003P, etc., have been generally used as printing aluminum alloy material plates. Such printing material plates are typically produced by a method wherein an ingot which is obtained by a semi-continuous casting process and the outer surface of which is then removed by scalping (removal of the outer surface), is heated to a predetermined temperature and then hot-rolled after being subjected, if required, to a uniformalizing treatment (treatment to provide homogeneities), thereafter, the thus processed ingot is cold-rolled at a reduction rate of plate thickness of from 20 to 95% so as to obtain a rolled plate of an intermediate thickness. Alternatively, the ingot is directly cast by a continuous casting process to obtain a coiled sheet having a plate thickness of 12 mm or less, and is then subjected directly to a cold rolling process so as to obtain a rolled plate of intermediate thickness with no heat-rolling process being applied thereto, and the plate of intermediate thickness, after being subjected to an intermediate annealing process, is subjected to a final cold-rolling process at a reduction rate of from 20 to 95% in order to obtain necessary mechanical properties.
Upon actual use of the above-mentioned printing aluminum alloy material plate for printing, the material plate, which beforehand is surface-roughened by a mechanical process, a chemical process, and an electrochemical process, or a combination of two or more of these processes, and is then preferably subjected to anodic oxidation treatment, is coated with a photo-sensitive material and then is exposed, thereafter being developed, and the material plate is then subjected to a heat treatment at a temperature of from 250.degree. to 300.degree. C. in a short time (usually referred to as a "burning treatment") so that the strength of the photo-sensitized film is increased to enhance its printing press life and is wound around a cylindrical plate drum, whereafter printing is conducted on sheets of paper after ink for printing is applied to the image area of the material plate in the presence of dampening water and is then transferred to a rubber blanket.
Printing aluminum alloy material plates to be used as mentioned above are required to having the following characteristics (A), (B), and (C):
(A) A uniformly roughened-surface can be formed by surface-treatment, no irregularity is brought about after surface-treatment, and a suitable color tone is exhibited. The ability of being able to be subjected to such uniform and appropriate surface-roughening treatment is hereinafter referred to as "surface-treatment ability";
(B) Lowering in strength as a result of the burning treatment should be small. Such an ability is hereinafter referred to as "burning ability"; and
(C) No ink stains occur on non-imaged area during printing. This ability is hereinafter referred to as "ink stain resistivity".
Of these above-mentioned characteristics, if the surface-treatment ability (A) is inferior, the tone of the surface-roughened material plate is excessively whitish or blackish, and, in certain cases, has irregularity in color which results in lowering the commercial value of the material plate. Since the surface-roughened after surfaceroughening significantly affects the printing press life and the image sharpness and clearness satisfactory surface-treatment and the uniform roughness after surface-treatment are very important conditions to be achieved for the printing plate. It is noted that in the case of surface-roughening treatment by electrolytic etching, the affect of the property of the plate material itself (surface-treatment ability) is, of course, not negligible in view of the electrochemical reaction between the outer surface of aluminum and electrolyte, although the condition of the roughened surface is naturally changed with great variety depending upon the electrolytic conditions and the type(s) of electrolyte employed. However, the conventional printing aluminum alloy material plates have not been fully studied concerning the surface treatment ability for surface-roughening, and, therefore, may not always have a sufficient surface-treatment ability from a practical viewpoint.
Concerning the burning ability (B), Japanese Patent Publication Nos. 27243/69 and 274244/69 describe in detail that an image area can be effectively reinforced by such a method that a PS plate having an aluminum alloy plate as a base material which is beforehand exposed and developed by a conventional process, is subjected to heat-treatment (referred to as a "burning treatment") at a high temperature. The heating time and temperature for such burning treatment depend upon the type of resin forming the image area, but are, as a rule, within a temperature range of from 200.degree. to 280.degree. C. and a time limit of from 3 to 7 minutes. However, burning treatment at a higher temperature has recently become desirable in order to enhance the printing press life as well as to shorten the time necessary for the burning treatment. However, if a conventional aluminum alloy material plate is heated at a temperature 280.degree. C. or more, recrystallization occurs, resulting in extreme lowering of the strength of the plate. Therefore, when such aluminum plate is used as a support for lithographic prinitng plates, there are problems in that handling of the prinitnig plate is very difficult. It becomes impossible to mount the printing plate on a priniting cylinder of a press, and it is impossible to make resistering the printing plate in the case of multicolor printing. In view of this disadvantage, the development of new aluminum alloy material plates which are high in heatresistivity and a printing aluminum alloy which is excellent in burning ability, has been eagerly desirable.
Ink stain resistivity is essential to printing plates, since stains on printed matter due to adhering of ink to the non-image area of the printing plate should be avoided. However, in conventional printing aluminum alloy material plates, study of the ink stain resistivity has been not sufficiently conducted, and therfore, no practical solution has been discovered to overcome such an ink stain problem until now. The inventors have studied the problem of ink stain and found that this problem is mainly caused by localized corrosion which is caused by a chemical reaction between the printing plate and dampening water. Accordingly, the inventors have discovered that this problem of ink stains can be overcome by suitable selecting the material compositions of the printing plate.